In recent years, vertical LED has become a hot topic for research and development. In comparison to traditional standard and flip-chip structures, the vertical LED, with the combination of techniques such as wafer bonding, electroplating or laser lift-off (LLO), allows transfer of the epitaxial layer from the growth substrate to metal or semiconductor substrate with good electric-conduction and heat-conduction performance. The resulting upper and lower electrode distribution and vertical current injection can overcome a series of problems such as poor heat dissipation, uneven current distribution, poor reliability due to horizontal electrode distribution and side injection of current in the standard and flip-chip structure LED elements.
In fabrication of traditional vertical LEDs, the wafer bonding is made by applying high pressure and high temperature on the metal. More specifically, the process may include bonding the epitaxial layer coated with Au, Au—Sn, or other easily-bonded metal on the conductive substrate, similarly coated with metal; removing the growth substrate, and fabricating the N electrode to form the vertical LED. FIG. 1 is a schematic diagram for the vertical LED structure according to the above method, wherein the N electrode is at the top, which will block and absorb the light emitted from the active layer.